No satisfactory method exists to repair the damage caused by neuropathies, such as may be attributable to Parkinson's disease (Parkinsonism) or stroke. Parkinson's disease is a syndrome consisting of neurological deficits such as tremor, rigidity, brady- and hypokinesia, and other deficits in equilibrium and posture. Parkinson's disease is often associated with the aging of the nervous system. Similarly, stroke can affect the motor system, rendering the patient with symptoms of hemiparesis or paralysis.
The substantia nigra is the principal site of pathology in Parkinson's disease. Pigmented neurons of the substantia nigra project widely and diffusely to the caudate-putamen (corpus striatum) and are specialized to synthesize and release dopamine. Symptoms of Parkinsonism emerge when 75-80% of the dopaminergic innervation is destroyed. Patients with Parkinson's disease respond to dopamine replacement therapy. Unfortunately, the efficacy of dopamine replacement therapy decreases progressively with continued degeneration of the nigrostriatal dopaminergic pathway.
The identification of stem cells has stimulated research aimed at the selective generation of specific cell types for regenerative medicine. Although protocols have been developed for the directed differentiation of stem cells into therapeutically relevant cell types, such as dopaminergic (DA) neurons for the treatment of Parkinson's, motor neurons for the treatment of ALS, and oligodendrocytes for the treatment of MS, the efficient generation of substantial numbers of these cell types from stem cells has not yet been reported. The ability to generate unlimited numbers of DA neurons that express the full complement of midbrain DA neuron markers is an important part to providing a cure for Parkinson's. Thus, agents that can be utilized to stimulate the differentiation of stem cells to the DA lineage provide a potential to harness and differentiate both exogenous and endogenous stem cells for Parkinson's as well as stokes affecting the middle cerebral artery (MCA) and its branches.
In other cases, attempts to counteract the effects of acute or neurodegenerative lesions of the brain and/or spinal cord have primarily involved implantation of embryonic neurons in an effort to compensate for lost or deficient neural function. However, human fetal cell transplantation research is severely restricted. Administration of neurotrophic factors such as nerve growth factor and insulin-like growth factor also have been suggested to stimulate neuronal growth within the central nervous system (CNS). See, e.g., Lundborg, Acta Orthop. Scand. 58: 145-169 (1987); U.S. Pat. No. 5,093,317. Administration of neurotrophic factors to the CNS requires bypassing the blood-brain barrier. The barrier may be overcome by direct infusion, or by modifying the molecule to enhance its transport across the barrier, as by chemical modification or conjugation, or by molecule truncation. Many growth factors from the TGF-beta superfamily [Kingsley, Genes & Development 8 133-146 (1994)] and the literature cited therein are relevant for a wide range of medical treatment methods and applications which in particular concern wound healing and tissue regeneration. Some of these multifunctional proteins also have survival promoting effects on neurones in addition to functions such as regulation of the proliferation and differentiation in many cell types [Roberts and Sporn, Handbook of Experimental Pharmacology 95 419-472, eds. Sporn and Roberts (1990); Sakurai et al., J. Biol. Chem., 269 14118-14122 (1994)]. Thus for example trophic effects on embryonic motor and sensory neurones were demonstrated for TGF-beta in vitro [Martinou et al., Devl. Brain Res., 52 175-181 (1990); Chalazonitis et al., Dev. Biol., 152 121-132 (1992)]. In addition effects promoting survival were shown on dopaminergic neurones of the midbrain for the proteins TGF-beta-1, -2, -3, activin A and GDNF (glial cell line-derived neurotrophic factor), a protein which has structural similarities to TGF-beta superfamily members but these effects were not mediated via astrocytes [Krieglstein et al., EMBO J., 14, 736-742 (1995)]. The occurrence of proteins of the TGF-beta superfamily in various tissue and developmental stages corresponds with differences with regard to their exact functions as well as target sites, life-span, requirements for auxiliary factors, necessary cellular physiological environment and/or resistance to degradation.
GDF5 is expressed in the neonatal rat midbrain, suggesting that it may play a role in the development of dopaminergic neurons [Krieglstein et al., J. Neurosci. Res., 42 724-32 (1995)]. In vitro studies have demonstrated that MP52 has survival-promoting actions on embryonic rat dopaminergic neurons protecting them against the toxin 1-methyl-4-pyridinium (MPP+). Moreover, in vivo studies have demonstrated that intraparenchymal injection of GDF5 protects the adult rat nigrostriatal dopaminergic system from death induced by 6-hydroxydopamine (6OHDA) lesion of the medial forebrain bundle [Sullivan et al., Eur. J. Neurosci., 233 73-6 (1997)]. However, while such studies indicate that GDF5 appears to play important roles in the development and protection of the dopaminergic limbic system, they do not address or shed any light on the relevance of GDF5 with respect to neuroregenerative capacity or the ability to differentiate endogenous or exogenous cell populations.
Accordingly, there is a need for treatment of neurological deficits resulting from injury or disease to the striatum or substanta nigra pars compacta of a human.
The present invention seeks to utilize human recombinant GDF5 in a manner that enables the treatment or prevention of such resulting deficits.